Conventional Lead-Acid Batteries
Conventional lead-acid batteries generally consist of a series of separate (monopolar) positive and negative electrodes, connected in a combined series and parallel arrangement to achieve the desired voltage and current. Each electrode usually consists of a grid constructed of lead, (Pb), or a lead alloy which is filled with and covered with the active electrode material (lead dioxide for the positive electrode and sponge lead for the negative, in a fully charged battery). The purpose of the grid is twofold: to contain the active material so that the electrodes may be suspended in the sulfuric acid electrolyte solution, and to collect and to conduct the electrical current generated by the active materials, so as to be transferable to the outside of the battery. The grid is ordinarily constructed of lead (Pb) metal for four reasons:
(1) it is electrically conductive; PA1 (2) it is resistant to corrosion in the sulfuric-acid electrolyte solution; PA1 (3) the metal is relatively inexpensive (as compared to more resistant but unaffordable materials such as gold or platinum); and PA1 (4) it has exceptionally high gassing voltages for both hydrogen and oxygen, which minimizes the electrolytic decomposition of water in the electrolyte, and maximizes the formation efficiency of the active electrode materials (lead and lead dioxide). PA1 (1) the excessive weight required to achieve high-power discharges needed by electric vehicles; PA1 (2) the excessive weight required to store appreciable energy; and PA1 (3) the batteries have insufficient life to be economical.
The construction of conventional lead-acid batteries results in a number of problems which limit their usefulness in two important applications: electric automobiles and electric utility energy storage. The three main problems of prior lead-acid batteries are:
The excessive weight of lead-acid batteries is due to the extensive use of lead, one of the heaviest natural materials. The power of lead-acid batteries is largely limited by the use of a grid design to collect and conduct the electrical current, which forces the current to travel along a high resistance path thus limiting the useful power from the battery.